If you ask my personal opinion, I think that alien life is probably pretty
common in the universe. It's entirely plausible that it exists within our own
solar system, perhaps on Europa one of the moons of
Jupiter, which is thought to have a vast ocean underneath it's icy surface. But by
alien life, I mean life like bacteria, molds, and other one celled creatures.
I think complex intelligent life, like mammals, birds, and lizards is probably
very rare. And super intelligent spacefaring life-forms, like humans, is
probably exceptionally rare. But this is not to say they don't exist. But whenever
you read about alien visitations, or see alien creatures in the movies, they're
depicted as looking almost like humans. They may just have bigger eyes, or bigger
heads, or they look like some other animal that we're already familiar with
on earth. This is a good reason to be highly suspect of any claims of alien
visitations because aliens are highly unlikely, or near impossible, to look
anything like us. Why?...because aliens on another planet
would evolve in a completely different trajectory, under a completely different
set of environmental conditions, and circumstances, and are not at all likely
to look anything like us, despite what you see in the movies. In fact, they may
look so different, that we may not even recognize them as life-forms at all. So
if aliens really did visit us, what would they really look like from a science
perspective? The explanation is coming up right now...
Guys before we talk about life on other planets, I want to tell you something
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in the description. To understand what life on other planets may be like, first
let's look at the raw ingredients that life has to work with in the rest of the
universe, compared to our solar system. The most common elements in the universe
are, in order, hydrogen, helium, oxygen, neon, nitrogen,
carbon, silicon, magnesium, iron, and sulfur. And in our solar system, it's almost
exactly the same. So as you can see from this chart, our solar system is
essentially made of the same elements that the rest of the universe is made of.
So in that sense there's nothing special about the elements available in our
local group of planets, and our Sun. And the most common elements on earth are
iron, oxygen, silicon, magnesium, and carbon. So Earth is composed more of the heavier
elements than the rest of the solar system. Why would this be the case? Earth has
relatively modest gravity compared to the Sun and some of the heavier planets,
like Saturn and Jupiter. It's not able to hold on to much hydrogen, helium and
other lighter elements which tend to float away from its gravity. It should
not be surprising, then, that the lightest elements, such as hydrogen and helium, would be
more concentrated in the Sun and the more massive planets, like Jupiter and
Saturn. But the key element of life is carbon. Carbon is the backbone of
every known biological molecule. Carbon can form four bonds with other atoms
simultaneously. This makes it well suited for long chains of molecules that serve
life, such as DNA. Organic chemistry, or the chemistry of life on Earth, is based
largely on carbon. Is this unusual? Is this what we would expect to see on
other planets of the universe as well? You might look at the composition of
Earth and say, "well there's a lot more silicon available on earth." And if you
look at the periodic table, silicon is in the same family of elements as carbon. So
why can't alien life be based on silicon? This seems plausible, but when you look
more closely at the properties of silicon, you realize why life chose
carbon instead of silicon, even though it is about a hundred and fifty times more
abundant. The four bonds on carbon are all about the same strength and
stability. With silicon, the first bond is stronger than the rest, so this causes
instability of certain chemical reactions with silicon. In other words,
carbon is capable of forming large complex chains of molecules like DNA.
Silicon is not. It is unstable. So the complexity required for organic
chemistry with silicon is just not there. Carbon is also such that its bond with
other atoms, such as nitrogen, hydrogen, and oxygen is about the same strength. So
it's relatively easy for carbon to react with a variety of other elements. In
other words, it is a more reactive atom for chemistry. Silicon is just not as
reactive with other elements, and not as stable in large molecules. And given that
life chose carbon, when silicon was much more available to us on earth, advanced
life based on silicon instead of carbon is unlikely. besides carbon, what does
life on Earth have in common? All life uses liquid water as a solvent, and
adenosine triphosphate, or ATP, to store and release energy. It's likely that if
life on other planets is based on carbon, it will also need some type of energy
molecule, either ATP or something similar. But does it necessarily need water?
Water is the most abundant compound in the universe. This should come as no
surprise, because it's made up of hydrogen and oxygen, the first and third
most abundant elements in the universe. It's a good solvent because it's liquid
over a large temperature range. Everywhere there's water on earth, life
is also there. So life based on water could be quite common. Ao far, it would
not be a bad bet to presume that intelligent alien creatures on other
planets could be based on carbon chemistry, and water. This is not to say
that chemistry could not exist in other solvents, such as liquid ammonia, or
methane, which is prevalent for example on Titan, one of Saturn's moons. But from
what is known about earthly chemistry, it likely would not harbor complex
intelligent life. Would aliens be in the same environment as Earth?...Probably not
identical. But temperature-wise, Earth is unique in the solar system because it is
the only planet or moon where water can be found in three different phases, solid,
liquid, and gas at the same time. So for example, if you're sailing on a ship on a
foggy day, and see an iceberg, you're viewing water in all three phases at the
same time. There is a critical zone, or distance from the star where a planet is
not so hot such as mercury, where it gets so hot that water boils away, but also not
too cold ,where water freezes. This is crucial for life because liquid water
provides the medium, or solvent, in which complex organic chemistry can take place.
This can't happen in ice, and it so happens that the boiling point of water,
100 degrees Celsius, is close to the upper limit of organic chemistry. So if
our planet was too hot, organic chemistry would not work. But our alien planet
could certainly have a different ratio of water to land. And it could have a
different gravity. According to the latest Kepler data, there appears to be
many more planets bigger than Earth than there are the same size as Earth. So
there's a larger prevalence of so-called "super Earth's" in our galaxy. These are
planets about 1.25 to 2 times the size of Earth, and would have gravity about
two times to eight times that of Earth. But it's not known whether these are
rocky planets, like the earth and Mars, or gas giants, like Neptune or Uranus. So
for now, let's presume that we would need a planet similar to earth in size, and
perhaps 0.9 times to 1.1 times the size of Earth. Given the size of the galaxy,
with 200 billion stars, such a narrow range of planets would still be
plentiful - in the millions. So let's look at what life would be like on an earth-like
planet, in the habitable zone of a sun-like star, based on carbon chemistry
and water. To do this, I've teamed up with astrobiology authority, and zoologist
Biblaridion. Check out their YouTube channel Biblaridion for more stuff like
this. Here's him: We can be pretty certain that
some of the tendencies we see in organisms on Earth will be universal.
Some life forms would gain energy from star light, like plants, while others
would survive by feeding on other organisms, like animals. In the latter
case, these life forms would need a way of taking in nutrients and expelling
waste, which may take the form of a body cavity, with separate openings for
feeding and excretion. More complex animals will also have some way of
sensing and reacting to their environment, the analogs of eyes, ears and
noses, which would form the equivalent of a nervous system. In particular, eyes have
evolved many times among completely unrelated lineages. For example, the eyes
of octopuses, scallops, insects and mammals, are all thought to have evolved
independently of each other, but still serve the same essential function. So it
seems likely that eyes might be common on alien worlds as well. But alien eyes
might be sensitive to different wavelengths than our own, since they will
adapt for the peek spectrum of their own Sun ,which may be different than Earth's.
So they might see the world in a very different variety of colors than we do.
They might be able to see into the ultraviolet range, like many birds and
insects, or to sense infrared, to detect the body heat of other animals, like pit
vipers or vampire bats. However their eyes work, they would most likely need
more than one, since having multiple eyes would allow them to sense direction and
depth. Animals on earth have anywhere from two eyes, like in most vertebrates,
to over a hundred, like in some bivalves. Another trait found in virtually every
lineage of complex animals is a symmetrical body plan,
whether it's radially symmetrical like in starfish and jellyfish, or bilaterally
symmetrical like in arthropod and vertebrates. This symmetry is almost
always accompanied by cephalization, the concentration of the nervous system and
the mouth towards one end of the body, forming a sort of head. So it seems quite
likely that like many animals on earth, a complex alien body plan would exhibit
some form of symmetry, and have a distinct head-like region of the body
that bears at least two eyes and a mouth. When it comes to intelligent life as we
would classify it, the organisms would obviously need a
large brain capacity and the ability to learn new information to form a culture.
They would need some way of transmitting learned information from generation to
generation, and to communicate and cooperate with other individuals, like a
language. Their language might not be based on sound like human languages are,
but perhaps involve other modalities, such as movement - like sign language,
pheromones, changes in skin color, or texture, or even a combination of all of
these. To build the tools and structures necessary for an advanced civilization,
they would also need a means to manipulate the environment around them,
such as limbs, or digits of some sort, to handle objects and probably the ability
to perform fine motor movements. These need not be fingers, but anything that
can hold objects, perhaps prehensile tentacles, tipped with smaller digits. Do
they live in the sea? In the clouds of a gas giant? Or on land? Using our one data
point of Earth, there is no complex life that lives permanently in the atmosphere.
And most intelligent species on earth happen to be on land instead of the sea.
You might say, "what about dolphins and killer whales?" You have to remember that
these animals were once land mammals (evolved on land). They went back to live in the sea. That's
why they still need to breathe air. Does living on land provides some kind of
evolutionary bias towards higher intelligence? According to physics
professor Bernard Bates, at the University of Puget Sound, aliens with
advanced technology would have to be on land because technology needs fire to
kick-start it, by providing a survival advantage, and a way to create advanced
hunting tools. This can't happen in water. Light from the sun
also does not penetrate as deeply in oceans. There's very little light beyond
200 meters in the ocean. So the energy that ocean creatures have to work with
is less than the energy available on land. This makes it harder for larger,
complex creatures to evolve. Once again, here's Biblaridion: So if an alien
species lives on land, it would also need some means of terrestrial locomotion.
Limbless creatures might slither like snakes, or use muscular ripples like
gastropods or worms. But on earth, both vertebrates and arthropods independently
evolved legs, which are much more efficient and allow for greater speed
and maneuverability, than other forms of locomotion. So any land dwelling aliens
would likely do the same, if they have suitable structures available to adapt
into walking limbs. Having evolved from a 4 fin ancestor, most vertebrates have
four legs. Though some, like humans, kangaroos, and dinosaurs walk on just two,
while arthropods can have anywhere from six to several hundred legs.
However there is a trade-off here when it comes to optimal limb configuration.
the more legs an animal has, the more stable it will be, but the more energy
will be needed to power and coordinate the limbs, making running less efficient,
especially at large body sizes. It could be that large active animals are biased
towards a smaller number of legs, though this is difficult to say with any
certainty. This trade-off is especially relevant to predators, which need limbs
that have specialized for efficient running to catch prey. Often predation
also involves complex behaviors such as stealth or cooperative hunting, which
demands a greater intelligence. In humans, the evolution of a larger brain occurred
alongside a shift to a more predatory lifestyle. So intelligent aliens may also
descend from predatory ancestors, and therefore, might tend to have a smaller
number of walking limbs that are designed for efficient high-speed
movement. There are probably only so many ways an alien can efficiently see, eat,
walk, and communicate. And natural selection on their planet would probably weed out
inefficient body plans. How prevalent is intelligent life likely to be in the
universe? Dr. Yael Kissel, scientist at NASA's Ames Research Center, and other
scientists believe that most life in the universe,
as a whole, is likely to be microbial. But does simple life like
bacteria inevitably involved into more complex intelligent life? Well it's
important to realize that evolution doesn't have any end goal. It simply
selects for whatever traits provide an immediate advantage. In fact, in some
contexts, evolving to become more intelligent might actually be a
detriment to some species. For example, predators such as wolves and big cats
have achieved a relatively high level of intelligence, compared to other animals.
But if they became any more intelligent, the enormous energy demands of
supporting a large complex brain may outweigh the benefits it provides. So
further intelligence may not be selected for. Human intelligence, which is far
beyond any other living thing on earth, and which needs to be supported by a
huge energy investment, not only by our metabolism, but also by our culture, and
technology, may be an aberration and not advantageous outside a very specific set
of evolutionary circumstances. So we may be an exception in evolution, or the
result of a series of coincidental mutations in our ape genome. But given the
vast numbers of planets in the universe, it seems that even if our intelligence
is an accident, takes a long time, requires circumstances like being just the right
size planet, located at just the correct distance from its star, having a large
moon to balance our seasons, and being in a stable part of the galaxy where we
didn't get wiped out by a meteor or gamma burst, we should still have
company, intelligent neighbors somewhere! They are likely, however, to be so far
away that we may never actually encounter them. Seth Shostak, astronomer
the SETI Institute, believes that our first encounter with aliens will likely
not be with carbon-based life, but silicon-based life. He says that because
he believes that our first close encounter will not be with biological
creatures, but with their highly intelligent machines, or probes, that use
silicon chips for processors. They would have sent these out to the far reaches
of the galaxy. This makes sense if you consider that this is also the likely
evolution of us here on earth. We are much more likely to send probes to our
nearest neighbor, Proxima Centauri, 4.5 light-years away, for example, than
humans. So the next time you see little green men in movies, realize that this is
probably fantasy. Life-forms that we encounter would be completely different
than us. They might be little. They might be green.
But they will almost certainly not be men. Guys if you want more of this stuff,
then check out the Biblaridion channel at the link in the description. And if
you like this video give us a like and leave me a question, because I try to
answer all them. I will see you in the next video my friend...